Field of the Disclosure
The present application relates to a touch screen display device.
Description of the Related Art
With development of various portable electrical appliances such as mobile communication terminals, notebook computers and so on, demands for display devices being applied to the portable electric appliance are being increased. Liquid crystal display (LCD) devices among the display devices gradually widen application fields because of their features of easy mass production, easy driving means and realization of high image quality and large size.
In general, the LCD device includes lower and upper substrates which are combined with each other in such a manner as to face each other with having a liquid crystal layer therebetween. The LCD device controls transmittance of light penetrating the liquid crystal layer of each pixel according to a data voltage, in order to display an image corresponding to an image signal.
Recently, the LCD devices are being manufactured in such a manner as to provide functions of well-known input devices such as a mouse, a keyboard and so on. To this end, a touch screen allowing a user to direct input through it using one of a finger and a pen is being applied to the LCD device.
The touch screen is being applied to monitors of navigation systems, industrial terminals, notebook computers, financial automation equipment, game consoles and so on. Also, the touch screen is being applied to potable terminal such as mobile phones, MP3s, PDAs, PMPs, PSPs, mobile game devices, DMB receivers and so on. Moreover, the touch screen is being applied to home appliances such as refrigerators, microwave ranges, washing machines and so on. In this manner, the application field of the touch screen with an easy manipulation property is being widened.
For slimness of the LCD device with the touch screen, an LCD device including a liquid crystal panel with a built-in touch screen is being developed. Also, touch sensors being built into the display device such as an LCD device or an organic light emitting display device are being developed in an in-cell type. The in-cell type touch sensors include a photo touch sensor and a capacitive touch sensor. The photo touch sensor can recognize a touch on the basis of intensity of light sensed by a photo transistor. The capacitive touch sensor can recognize a touch based on a variation of the capacitance. More specifically, the photo touch sensor senses a loss current of the photo transistor, which varies along the quantity of light being intercepted or reflected by a touch object, and recognizes a touch. The capacitive touch sensor recognizes a touch by sensing a variation of the capacitance which is generated by the movement of electric charges toward a touch point when a conductive material such as a part of a human body or a stylus pen touches it.
FIGS. 1 and 2 are views schematically showing a touch screen LCD device of the related art.
As shown in FIG. 1, the related art LCD device with a built-in touch screen includes lower and upper substrates 10 and 20 which are combined with having a liquid crystal layer (not shown) therebetween. The LCD device adjusts transmittance of light penetrating the liquid crystal layer of each pixel according to a data voltage, in order to display an image corresponding to an image signal. Also, the LCD device detects a touch position TS using the variation of a capacitance Ctc in accordance with a touch TS of a user.
The upper substrate 20 is configured to include a black matrix 30, color filters 40 and an overcoat layer 50. The black matrix 30 defines pixel regions opposite to a plurality of pixels. The color filters 40 include red, green and blue color filters which are formed on the pixel regions defined by the black matrix 30. The overcoat layer 50 is formed in such a manner as to cover the black matrix 30 and the red, green and blue color filters 40. Also, the overcoat layer 50 is used to planarize the surface of the upper substrate 20.
The lower substrate 10 is configured to include the plurality of pixels which are used to drive the liquid crystal layer and detect a touch TS of a finger of a user or the touch TS of a pen. The plurality of pixels is defined by data and gate lines DL and GL crossing each other. Each of the pixels includes a common electrode 60 receiving a common voltage and a pixel electrode used to apply the data voltage to a region of the liquid crystal layer (or a cell Clc). The common electrode 60 and the pixel electrode are formed from a transparent conductive material such as indium-tin-oxide ITO. Such a pixel forms an electrical field in accordance with the data voltage and drives the region of the liquid crystal layer (or the cell Clc). To this end, the data voltage is transferred from the respective data line DL to the pixel electrode by means of a thin film transistor TFT which is switched according to a gate signal on the respective gate line GLn.
Meanwhile, in a non-display interval when any image is not displayed, the LCD device detects a touch of the finger of the user or a touch of the pen by driving the common electrode 60 as a sensing/driving electrode for detecting the touch. More specifically, a touch capacitance in accordance with a touch is generated between the upper substrate 20 and the common electrode which are positioned over each pixel. A touch controller (not shown) of the LCD device detects a touch position by comparing the touch capacitance Ctc, which is generated by the touch, with a reference capacitance. Also, the touch controller outputs the detected touch position to the exterior.
In order to easily recognize the coordinates of a touch, the common electrode 60 used in the touch screen LCD device as a touch electrode can be divided into n horizontal common electrodes and m vertical common electrodes. The divided common electrodes 60 must be connected to one another in a display interval, but separated from one another in a touch recognition interval. The connection and separation of the divided common electrodes 60 can be performed by a common voltage multiplexer (not shown) on a printed circuit board which is disposed outside the panel. As such, the divided common electrodes within the panel are arranged in such a manner as to be separate from one another.
FIG. 3 is a timing chart illustrating problems of the touch screen LCD device according to the related art.
In order to enhance a touch report rate, the touch screen LCD device of the related art allows a display operation and a touch sensing operation to be divisionally performed by gate lines. The touch report rate is in inverse proportion to a total sensing time which is necessary to scan all sensing nodes within a touch screen. As such, the touch report rate decreases as the total sensing time lengthens. Also, the touch report rate means the number of touch coordinate values which are transferred during a single second.
The gate line division driving method can generate a line dim phenomenon in a boundary line between a touch sensing area and a display area (i.e., in a gate line which is scanned at a transition time point from the touch sensing operation into the display operation).
More specifically, in the display interval T1, a data voltage on a kth data line DLk is transferred to a pixel through a transistor, which is turned-on by a gate signal on a mth gate line GLm, and displayed on the screen, Also, another data voltage on the kth data line DLk is transferred to another pixel through another transistor, which is turned-on by another gate signal on a (m+1)th gate line GLm+1, and displayed on the screen. Sequentially, in the touch sensing interval T2, a ground voltage GND is applied to the data lines DL including the kth data line DLk. As such, a touch of a user can be detected thought the divided common electrodes. After the touch sensing interval T2, i.e., when the touch sensing interval T2 lapses, still another data voltage on the kth data line DLk is transferred to still another pixel through still another transistor, which is turned-on by still another gate signal on a (m+2)th gate line GLm+2, displayed on the screen. At this time, the voltage on the kth data line DLk must increase from the ground voltage GND to the still another data voltage, and a voltage difference between still another data voltage and the ground voltage GND must be large. As such, the data voltage charged into still another pixel must decrease. Due to this, an image fault such as a line dim is generated.